13 AUG 03
THE PEIABILITY OF CELOPHANE TO MICROORGANTIS!S
by
Wallace B. Tibbets, Jr.
Siritted in -partial fulfillment of the requirements for the
degree of
Bachelor of Science
from the
Massachusetts Institute of Technology
1931
Course VII
Signature of the A
.
......
-- 7
Prof. A. L. iHerrill,
Secretary of the Faculty,
Massachsetts Institute of Technologr.
Dear Sir:
I submit herewith
rr thesis in partial fulfillment of the re-
quirements for the degree of Bachelor of Science from the Massachusetts
Institute of Technology.
Yo.rs very truly,
1 761 7 5
ACI1OWLEDG1IT
The athor wishes to exoress his thanks to Professor S. C. Prescott
of the Department of Biology and Pu.blic Health for his helpful assistance
in the preparation of this thesis.
Alsothe author wishes to thank
Mr. R. C. Schilly and Mr. A. F. Link of the DuPont Cellophane Company,
Incorporated, for their cooneration in providing the materials for the
work.
To the American Tyne Culture Collection the author is also in-
debted for severa of the cultures of organisms used.
TAKLE OFBCOINTMTTS
Introdu~ction............................
Statement
of the
Problem.............
Laboratory Technique
1
...........
....
4
-
Midroscopic Examination........................6
Bacteriological Examination...........
Sterilization.........................
O6
Experimental Procedure........................9
Conclusions.................................15
Anmendix A Sheet of Plain Transoarent Cellophane......
Organisms Used in Tests,.................
.
Media Used in Test.................
A.dhesives....
............................
Bibliography................................0.24
23
THE PERMABILITY OF CELLOPHA= TO MICROORGANISMS
Introduction
The protection of foods against contamination during handling and
exposure for sale has greatly increased in recent years, and has led to
the development of numerous types of packing materials.
With the grow-
ing popularity of having foodstuffs so displayed wrapped so that the conlsumer can see the material he is buying, the desirability of having some
sort of transparent wrapper has become of increasing importance.
There
are several materials which have been used for this purpose and which
meet the requirements to some degree, but they all present certain problems in regard to the efficiency of protecting the product that is wrapped
in them not only from the dust and dirt which might be suspended in the
air, but from undue drying, and from the dangers due to the penetration
by microbic organisms.
One form of wrapping material that has been de-.
veloped through research and which has gained great popularity during the
past few years is Cellophane.
The present study is an inquiry into the
possible permeability of this material to certain types of microorganisms.
The word "cellophane" is the trade name for a regenerated cellulose
film made by the DuPont Cellophane Company, Incorporated, and its popurlarity lies in the fact that it is transparent, lustrou±s, durable, flexible, and impervious to air.
A brief history of its manufacture is given.
Spruce pulp of the finest grade is the basic ingredient.
This pulp
is dissolved in a caustic soda solution and carbon bisulfide is then added
to produce what is kIown as a cellulose xanthate.
To this is then added
-21.
a dilute solution of caustic soda and the resulting solution is known as
viscose.
After passing through a filtering and air removing process
this viscose is then cast in a bath of sulp1ric acid and sodium sulohate
from which it emerges as a film.
It is then washed and desulphonized
by the use of sodium sulphide and goes through a bleaching solution of
sodium hypochlorite.
This film is then passed through pure glycerol
which is adsorbed and tenaciously retained by the film, thus imparting
softness and pliability.
This completes the process and the finished
film is run over drying rolls and is wound on cores into rolls of any desired weight.
This final sheet of Cellophane is approximately nine ten-thousandths
of an inch in thickness, but greater thickness up to seven one-thousandths
is available.
To provide a suitable wrancing material for products having a high
moisture content or where it is desirable to protect then against moisture
from outside sources, a special Moisture-proof Cellophane has been develoned.
This product is
Plain Transparent Cellophane that has been
orocessed with a microscopically thin coating of waterproofing substance
which does not appreciably increase its thickness.
That this Moisture-proof Cellophane does retain or exclude moisture,
as the case may be, is shown by the following table;
-3-.
Diffusion of Water
Tanor at 1000F,
Materials
Moisture-proof Cellophane
270 mg/m2 /hr.
Waxed brown paper
400
"
Waxed glassine paper
530
"
Average of fifteen waxed papers
2,000 "
"
Plain Transparent Cellophane, of course, is not moisture-proof and
is used in many cases as a sem-permeable membrane for dialysis of salt
solutions in the separation of proteins and similar work.
Cellophane has a very high tensile stren-gth being stronger than a
good all-rag bond paper and having as high a bursting strength as the
highest grade paper.
Optically, Cellophane is exceptionally transparent not only to the
visible spectrum but also it passes 70 of the ultra-violet waves in the
curative region of 2900 to 3100 Angstrom units.
Unlike the special ulta-
violet transmitting glasses which lose a large fraction of their transparency on prolonged eposure to ultra-violet rays, the transparency of
Cellophane decreases but slightly after an exposure to sunlight for a
year.
Cellophane finds an application in all phases of life and industry.
It is used as a utility wrap on a variety of products, including baked
goods, meats, frozen foods, fruits, confections, nuts, coffee, textiles,
tobacco, and drugs.
Each year the uses are extended into a new field
so that the demand for both varieties,
parent, is constantly increasing.
oisture-proof and Plain Trans-
-4Statement of the Problem
Because of the wide armlication of Cellophane in the food industries
as a wrap for finished products, this material becomes one which concerns
the public health.
Therefore the object of this work is to determine
the permeability of Cellophane, both Moisture-proof and Plain Transparent,
to microorganisms under various conditions.
Packages wrapped in Cellophane seem to be kept in a condition free
from invasion by microorganisms which might cause spoilage, but the questions that naturally arise are of great importance.
Would it not be possible for microorganisms to gain entrance to some
product wrapned in either variety of Cellophane through some means as yet
unaccounted for?
Can Cellophane, as such be decomoosed by the action of some cellulose-attacking organism and thus give entrance to the product?
In order to answer these questions it is necessary to resort to
laboratory experimentation.
I, therefore, carried out the following ex-
aminations:
1. The Cellophane was examined microscopically for the presence of
pores, voids, or holes of such a nature that would allow passage of microorganisms.
2. It was then put through bactericlogical examinations to determine
to what extent the sheets were contaminated as they were received.
3. Sterilization procedubres were performed in order to determine the
best method with which this Cellophane could be treated.
4. Various tests were attempted in order to determine the permeabili.
ty of the material under test.
-5Hence, the following discussion deals with the laboratory technique,
the results obtained by the various experiments, and the conclusions that
were drawn from the data obtained.
-6Laboratory TechzziMe
Microscopic gxamnation
The Plain Transparent Cellophane was examined unler both high and
low power with a microscope and it was found that a definite grain can
be identified.
This grain is due to the manner in which Cellophane is
cast in the process of manufacture.
After strict search of several sheets selected at random from the
stock supply no pores, holes, or any other means of passage through the
sheets could be seen.
Bacteriological Examination
Several sheets of both Moisture-proof and Plain Transpnarent Cellophane were again selected at random, care being taken to contaminate them
as little as possible.
They were therefore handled with sterile tweezers
and were cut into small pieces (about 1" x 2") with sterile scissors.
These cut pieces were then laid on sterile agar plates and were incubated
at 200C. and 370C. for 48 hours.
At the end of this time they were ex-
amined and from the 12 plates examined four microorganisms were taken.
A pair of control plates that had been exposed to air for five minutes
were run for the same length of time and at the same temperature and from
these plates six organisms were isolated.
Upon comparison three of the
organisms found on the Cellophane checked with three of those isolated
from the air so it was deduced that the contamination on the Cellophane
was that normally found in the air or the dust particles.
Sterilization
Because of the fact that these sheets of Cellophane were slightly
-7contaminated it was thought best to carry out various methods of steri-.
lization in order to facilitate the observation of results of the later
experiments.
An attempt was first made to sterilize the Cellophane by boiling it
in water.
Several small pieces were dropped in the water and a check
was kept on the temperature.
At 800C. the Celloohane began to appear
cloudy and above this temperature the cloudiness increased.
This was
repeated three times but each repetition was culminated by the same results.
This cloudiness was probably due to the precipitation of some
of the cellulose in the Cellonhane but whatever the cause it was an undesirable change, so this method of sterilization was discarded.
Following this, the usual method of sterilization in an autoclave
was attempted.
Sheets of Cellophane were put in an autoclave and were
kept at fifteen pounds pressure (about 249 0 F. or 1210C.) for forty-five
minutes.
At the end of this time they were removed and were found to
have become slightly discolored and clouded.
Their texture was changed
so that it was brittle and upon examination with a microscope tiny cracks
were visible.
This procedure was repeated with the same results.
As
this condition of the Cellophane might render the material unsuitable
for experimental work this method of sterilization was also discarded.
Sterilization by dry heat was then attempted by placing sheets of
Cellophane in a hot-air oven for one-half hour at a temperature of about
180OC.
At the end of this time the sheets were removed and examiined
and it was found that they were affected much the same as those which
had been sterilized by autoclaving, except that the brittleness had been
increased.
Therefore, this method of sterilization was also discarded.
Attempts to sterilize the material by means of alcohol were made in
the following manner: A solution of alcohol of approximately sixty percent strength was made uo and sheets of Cellophane were introduced and
allowed to stand for twenty-four hours.
removed and washed with sterile water.
At the end of this time it was
As was expected, the Moisture-
proof Cellophane had become milky and blistered due to the water and alcohol penetrating the waterproofing layer.
The Plain Transparent Cel-
lophane was found to be in good condition when it came out of the alcohol
but upon drying it became so wrinkled that it was entirely unsuited for
further work.
This wrinkling was due to the uneven stresses set up in
the sheets as they dried.
This same technique was carried out using the same concentration af
alcohol, but a much shorter time, varying from one-half minute to two
minutes.
It was found that in this case the material had not been suf-
ficiently treated as it was not sterilized.
This was determined by care-
fully washing off the excess alcohol with sterile water and after the
Cellophane had dried it was cut up and placed on poured plates of sterile
nutrient agar.
After 24 hours some growth was noticed.
While this
growth was less than that found with an untreated sheet, it was positive
and this served to cause this method of sterilization to be discarded
also.
The same difficulties were also encountered in drying and hav-
ing the sheets wrinkle.
Mercuric chloride was then used to sterilize the Cellophane, but
this attempt proved fruitless because of the strength of the disinfectant which caused a change to take place in the surface of the material.
It was therefore determined to attempt to carry out these permeabil-
-9ity experiments by means of some microorganisms which could be easily
identified and yet would not be confounded with those microorganisms
normally found in air.
Those organisms finally decided upon were:
Erythrobacillus prodigiosus, Sarcina lutea, Staphylococcus aureus, Bacillus violaceous, Pseudomonas aeruginosa, Bacterium tumefaciens, Bacillus cereus, Cellulomonas biazotea, and Aspergillus niger.
The Cellulomonas biazotea is an organism which will break down cellulose and It was thought that its action on Celloohane might be posi-.
tive.
The Aspergillus niger is a common mold and it was made use of to
determine the permeability of Cellophane to mold growths.
Experimental Procedure
Membranes of Moisture-proof Cellophane were stretched over the large
end of thistle tubes and the edges were cemented down with DuPont Cellophane Cement #559.*
After being allowed to dry for twenty-four hours
these were examined for tightness by filling them with sterile water.
Any that showed evidence of leakage were either discarded or repaired and
those that proved tight were used in the test.
Twelve seventy-five cubic centimeter portions of sterile nutrient
broth** were poured into 12 sterile 150 cc. beakers, to be used as the
base test medium.
Twelve five cubic centimeter portions of this nutri-
ent broth were then inoculated - three with a loopful each of Bacillus
prodigiosus, three with Bacillus violaceous, three with Sarcina lutea,
and three with Staphylococcus aureus.
These inoculated portions were
carefully introduced into the small, open end of the thistle tubes, precautions being taken to avoid spilling the inoculated broth on the out* ** See Appendix.
-10side of the thistle tube where it might contaminate the broth in the beaker and therefore snoll the observation.
A large cork that had been
previously bored to fit the stem of a thistle tube was treated with disinfectant to remove any contamination that it might harbor.
This cork
was then fitted on the stem of a thistle tube and was pushed down until
it reached the bulbous end.
This cork was so chosen that it just fit
into the beaker forming both a top for it and a stand for the thistle
tube.
The open end of the thistle tube was closed with sterile non-
absorbent cotton and the cork was sealed to the beaker with sterile paraffine.
This preparation was repeated for all twelve of the tubes.
These
corks all had a second hole bored in them through which a pipette could
be introduced and the medium in the beaker extracted.
plugged with sterile non-absorbent cotton also.
This hole was
The finished annaratus
is shown in Fig. I of the Appendix.
These prepared tubes were incubated at twenty and thirty-seven degrees Centigrade.
Observations were made hourly after eighteen hours.
After the above mentioned time it was noticed that the membrane was
becoming blistered due to the penetration of the water-proofing layer by
the liquid medium.
Up to this time sterility of the outside medium had
been maintained as was demonstrated by removing 1 cc. portions from time
to time and plating them out on nutrient agar and incubating at both 200
and 3700. for twenty-four hours.
No growth on these plates showed that
the inoculum had not penetrated.
After the blistering had started it was noted that the outer medium
was no longer sterile.
This was probably due to the fact that as the
membrane blistered it caused pinholes to form by the tearing action of
-11the sepcaration and the organisms found an easy exit from their hitherto
tight cell.
Results
Organism
0-18
19
B. prodigiosus
0
B. violaceous
0
Sarcina lutea.
0
0
Staoh. aureus
0
0
0
blister
Time in hours
21.
22
20
23
24
0 blister
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
blister
0
blister
Because of this blistering action this test was discarded as- being
performed under conditions which the material under test would never meet
in practice as there is no occasion to enclose liquid media in such a
limn container.
This same procedure was then repeated using the Plain Transparent
instead of the Moisture-proof Cellophane.
No penetraticn of this Cellophane was noticed even after ninety-six
hours, nor did a culture of Asnergillus niger inoculated in triplicate
in the same manner show any penetration.
Upon comoletion of this exoeriment a series of tests were conducted
which would simulate those conditions met in oractice with wrapped food
products and would give some definite data on how such preparations should
behave.
Tubes of Celloohane were made by rolling strips (3" x 6") around a
culture tube and the edges were cemented down with one of the cements*
used for this purpose.
* See Anendix.
This made a tube about three-fourths of an inch
-12in diameter and six inches in length.
After being allowed to dry for
twenty-four hours these tubes were then cut into two-inch lengths.
One
end of these short lengths was folded over and sealed with the cement,
thus forming a small bag which was found to be tight by allowing water
to stand in it for a short period.
These were dried out by means of
alcohol and ether and an air blast.
Tubes of sterile nutrient agar were then imersed in hot water for
a short time so that the agar would be softened next to the wall of the
test-tube and would be loosened.
The agar was then caused to slide out
into a sterile Petri dish where it
was cut with a sterile knife into
small nieces.
These blocks of agar were handled asentically by irmaling them upon
a sterile nichrome inoculating needle and carefully placing them in the
small bags.
The blocks were then inoculated superficially with one of
the test organisms and the bags were then placed on poured agar plates.
This was repeated in triplicate for check purposes with each of the test
organisms.
These prepared plates were then incubated at 200C. and ob-
servations were made every twenty-four hours.
The results of this experiment justified those obtained in the previous test in that the bacteria did not penetrate the Cellophane.
In
this case, however, the Aspergillus niger was noticed to be growing outside the bag.
After close examination it was found that this was caused
by water of condensation running out and carrying with it some of the
snores of the mold.
This water of condensation was due to some of the
moisture evaoorating from the agar and condensing on the Celloohane.
-13A modification of this method was then attemoted.
[I
Nutrient agar
was melted and poured into the small Cellophane bags until they were
filled about half full.
Here it was allowed to solidify and then was
inoculated with each of the various cultures on the exposed surface,
and by puncture with the inoculating needle in such a manner that the
agar became heavily inoculated with the organism.
These bags were then
placed on poured plates of agar and were incubated at 20 0 C.
This method was very similar to that used above but it was thought
that it would give a more severe test because of the greater surface of
the agar that would be in contact with the Cellophane, thus giving greater possibilities of penetration.
Again trouble was encountered with the open ends allowing the water
of condensation to run out and carry with it some of the organisms similar to the case cited above.
Of course, this made it difficult to de-
termine whether or not any penetration of the Cellophane had taken place.
Therefore, in the subsequent runs the ends of the bags were folded over
after inoculation so that any water that did condense would not run out.
These experiments showed that both Plain Transparent and Moistureproof Cellophane were imnenetrable to microorganisms.
The action of a cellulose solitting organism on Plain Transparent
Cellophane was then studied.
A culture of Cellulomonas biazotea Kel-
lerman was obtained and was put through the same experiments as have
been previously described.
All inoculations were incubated at 200C.
and as this organism acts more slowly than the others the time of incubation was prolonged.
Observations were made each day for eighteen days
and at the end of this time no penetration was evident.
It was there-
-14fore concluded that this organism would not eenetrate the Cellophane.
Another method was used to study the action of the various organisms but it proved to be inapplicable here.
Tubes of Cellophane simi-
lar to those previously described but of smaller diameter were made by
rolling Cellophane strips (2" x 3") about a three-inch test tube.
This
made tubes one-half an inch in diameter and three inches in length.
The overlapping edges were sealed with cement #559.
After these had
been allowed to harden for twenty-four hours they were considered ready
for further maninulation.
The bottoms of .three-inch test tubes were
cut off about one-half an inch from the bottom and the two parts so
formed were cemented into the Cellophane tubes in the manner as shown in
Fig. I1.*
These prepared tubes were then filled with nutrient broth and were
suspended in sterile nutrient broth contained in one hundred and fifty
cubic centimeter wide-mouth Erlenmeyer flasks.
The level of the two
liquids was then made equal to obviate an unequal pressure and the liquid
in the tubes was inoculated with the test organisms.
These were incu-
bated for twenty-four hours but unon first examination it
was found- that
the liquid had caused the cement to become loosened and that there was
free interchange of the liquids between the inoculated and sterile broths.
Several different seals were tried but they all turned out unsuccessfully.
Hence, this method was discarded.
* See Appendix.
-15CONCLUSIOITS
My results have clearly indicated 1. That both Plain Transparent and Moisture-proof Cellophane
are imoermeable to microorganisms under ordinary conditions, and as a
result they are both excellent wranping materials.
2. That the various methods of sterilization of Cellophane
which we tried are unsuccessful, as they all render it unsuited for test
purposes.
Other methods which I believe could be applied might give
favorable results but were not attemoted..
However, the natural bac-
terial flora on the Cellophane is so limited and its character is such
that it led to no great difficulty in carrying out these experiments.
It was my intention to carry these experiments further with
foodstuffs themselves.
This might be carried out by wrapping both fresh
and spoiling products in Cellophane and determining whether or not the
wranpings are permeable under these conditions.
It is probable that
such work would prove the same thing that has been shown in this thesis
but, on the other hand, some new and enlightening facts may be learned
regarding this material.
The reason that this Cellophane is impenetrable to microorganisms must lie in the fact that the process of manufacture is such that
no pores or interstices are formed thus giving no passageway for the
bacteria or molds to utilize.
The fact that it is very similar to vis-
cose (a sodium salt of cellulose xanthate) indicates that it would not
be broken down by a cellulose splitting organism since these act only on
pure cellulose.
APPEITDIX
-.16-.
YOU ARE ITOW LOOKINTG
THROUGH
A SHEli!I OF
PIAIIN TRANSPAREST CELLOPHAE
(0.00088 inch in thiciess)
-17Organisms Used in Test
#1
Erythrobacillus prodigiosus (Serratia marcescens Bizio)
Coccobacteria: 0.5 by 0.5 to 1.0 microns, occurring
singly or in pairs or in chains of 5 to 6 elements.
Gram-negative.
Motile, with peritrichous flagella.
Gray colony becoming red.
Gelatin: Liquefaction.
Agar Slant: White, smooth, moist, taking on a redorange to fuchsin color.
Indol: None.
Nitrates reduced to nitrites.
Aerobic, facultative.
Optimum temperature: 250 to 30*C.
Habitat: Water, soil, milk, and foods.
#2
Sarcina lutea
Spheres: 1.0 to 1.5 microns, showing packets in all
media.
Grami--ositivev
Gelatin: Slow liquefaction.
Agar Slant: Sulphur to chrome yellow.
Indol: Slight.
Nitrates generally reduced to nitrites.
Hydrogen sulphide formed.
Aerobic.
Optimum temperature: 250C.
-18.-
Staphylococcus aureus Rosenbach
Spheres: 0.8 to 1.0 microns, single, and in pairs, or
in irregular clumps.
Gram-positive.
Gelatin: Liquefied.
Agar Slant: Abundant, opaque, smooth, flat, moist,
yellowish to orange.
Indol: None.
Nitrates reduced to nitrites.
Slight hydrogen sulphide formation.
Pathogenic.
Aerobic.
Cotimum te merature: 370C.
Habitat: Skin and mucous membranes.
The cause of boils,
abcesses, etc.
Chromobacterium violaceum Bergey et al.
(Bacillus violaceous
Bergonzoni).
Slender Rods: 0.8 to 1.0 by 2.0 to 5.0 microns, occurring
singly or in chains.
Motile with peritrichous flagells.
Gelatin: Slight liquefaction.
Agar Slant: Deep, violet, spreading growth.
Nitrates not reduced.
Aerobic, facultative.
Ontimnm temperature: 250 to 300C.
Habitat: Water.
-19
Pseudomonas Aeruginosa (Schrater) Migula
(Bacillus pyocyaneus Gessard)
Rods: 0.5 to 0.6 by 1.5 microns.
Occurring singly, in
pairs, and in short chains.
Motile, possessing one to three polar flagella.
Gram-.
negative.
Gelatin: Rapid liquefaction.
Agar Slant: Abundant, thin, white, glistening, medium
turning greenish to dark brown or black.
Indol: Nor formed.
Nitrates are reduced to nitrites.
Aerobic, facultative.
Optimum temperature: 370C.
Habitat: Open wounds, old sinuses, intestinal tract,
sewage.
Pathogenic to rabbits, guinea pigs, rats,
and mice.
Phytomonas tumefaciens Bergey et al.
(Bacterium tumefaciens Smith and Townsend)
Rods: 0.6 to 1.0 by 1.2 to 1.5 microns in the infected
plant and 0.7 to 0.8 by 2.5 to 3.0 microns in agar,
occurring singly and in pairs.
Motile with one to three polar flagella. Rods white.
Grani-negati w.
Gelatin: No liquefaction.
Agar Slant: Moderate, filiform,
Indol: Formed in slight amount.
Nitrates not reduced,
.Uaerobic,
facultative.
Optimum temperaturet 250 to 2800.
Habitat: Causes "0rovn Gall" on the Paris daisy.
-20-
#7
Bacillus cereus Frankland.
Rods: 0.75 by 2.25 to 4.0 microns, occurring singly and
in chains.
Motile with peritrichous flagella.
Spores central, 0.8 to 1.0 by 1.125 to 1.5 microns.
Cells store glycogen as reserve material.
Gram-negative.
Gelatin: moderate liquefaction.
Agar Slant: Abundant, thick:, white, mealy, becoming yellowish white with pellucid dots.
Indol: Not formed.
Nitrates not reduced.
Aerobic, facultative.
Optimum temp)erature: 3000.
Habitat: Soil.
#8
Cellulorionas biazotea (Kellerman) Bergey et al.
Rods: 0.5 by 0.8 micron.
Mottle by means of one to
three neritrichous flagella.
Gram-negative.
Gelatin: Liquefied.
Agar Slant: Luxuriant, yellow growth.
Indol: Not formed.
Nitrates reduced to nitrites.
Acid in dextrose, lactose sucrose, maltose, glycerol,
and starch.
Aerobic.
Optimum temperature: 200C.
Habitat: Soil.
-:,>l.
DI-Amgg
co /o n P/Uff
T &le 7ik
Cellolohile
- Filhe
MC1nbrdt7e
Sectl'oI7,ol Dldgpd n of 71iisIle khe Prevaralioli.
1,rk111-e 2-,
0
117OC4,11d /1-1/ lawlllh
'do-01,11?
-22-
MediiaUsdinJe.
Rut rient Brop
Difco Nutrient Broth made un of three parts of Bacto-beef Extract
and five parts of Bacto-Pentone was used.
Eight grams of the above
coaoound was mixed thoroughly with one liter of distilled water which
was then placed in an autoclave and kept at a pressure of fifteen pounds
for twenty minutes.
tubed.
At the end of this time it was removed and was
The H-Ion concentration of the medium did not need adjuisting
as that was already taken care of im the preparation of the dry medium.
This was found to check with the reading given on the bottle: p-H - 6.6.
uTarient Agr
Bacto-Nutrient Agar is made up of the same ingredients as the nutrient broth with the addition of fifteen parts of Bacto-Agar.
The same
nrocedure of preoaration was carried out here as in the preparation of
the nutrient broth.
The nH of the medium is 6.5.
M'alt m&atAa
This medium is made -o of the necessary ingredients to give the
same reactions as would a true malt agar.
The ol when finished is 4.6.
Pet tone Soljuton
This solution was made un from Bacto-Peptone in the required manner and the pH of the finished product was found to be 7.1.
Nitrate
r
This agar is the same as the nutrient agar with the addition of one
part of potassium nitrate.
When prepared the pH was 6.7.
-23-.
Some trouble was encountered with the develaoment of an adhesive
that wo-uld stick the Moisture-proof Cellophane to itself and after casting about for some such material, it was learned that the DuPont Cellophane Comoany, Incorporated, had developed several Which would answer
the purpose.
Upon anlication to them, they were kind enough to send
samoles of #405, #466, #559, and Methyl-cellosolve.
These were all to
be used in connection with the work on Moisture-proof Cellophane.
For
the Plain Transparent Cellophane a sample of re.ilar Cellophane adhesive
was sent to the writer.
-24B&BLIOGR P
1. Hyden,
;W.L.,
1929.
Manufacture and Properties of Regenerated
Cellulose Films.
Ind. & Eng. Chem., 21, 405.
2. Norris, J. F., 1922.
Organic Chemistry.
McQ-raw-Hill Book Co.
3. Bernthsen, A., and
Sudhorouagi, J. J., 1931. A Text-book of Organic Chemistry.
D. Van Nostrand Co., Inc.
4. Bergey, D. H., 1925.
5. Second Report of the
Adhesives Research
Committee.
A Manual of Determinative Bacteriology.
The W1illioxns & Wilkins Co.
Dent. of Scientific and Industrial Re-search.
His Majesty's Stationery Office, England.